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Using adhesives correctly

Steve Thornton explains how to use adhesives correctly when it comes to the installation of LVTs.

WHEN LVT installations are planned, there are many factors to consider. The type of project and the usage of the area. Will it be a commercial installation or domestic? Will it be light foot traffic or heavy use? It’s also critical to understand the nature of the substrate, and what level of preparation may be required.

Another consideration is the orientation of the installation environment and the volume of natural light which may fall upon the floor. In some cases, when large format glazing is present and the orientation allows for long periods of sunlight to fall onto the floor, it’s exposed to significant rises in temperature, known as solar gain. When exposed to these significant rises, there’s obviously a significant fall in temperature once the sunlight fades, this is known as thermal cycling.

In these circumstances, the correct adhesive selection is a vital factor for a successful installation. There are many adhesive types on the market, and while many of them are suitable for use with LVT, some have more niche uses than others.

The function of the adhesive is to bond the floor covering to the floor. It’s very important when adhering LVT that there’s a strong bond, as modular flooring can suffer from dimensional change if not sufficiently bonded to the substrate. Inadequate bonding is the most common reason for LVT lifting away from the floor. Leaving an adhesive too long before placing the tiles doesn’t create the bond strength required, as the adhesive isn’t able to adequately transfer to the tile and generate the bond needed.

Preparation of the substrate is also critical when it comes to the use of flooring adhesives. In many instances, the floor will have been prepared with a smoothing compound, the ideal medium for applying adhesives onto. When a substrate isn’t prepared, problems can occur. Overly porous surfaces, like sand or cement screeds, will remove moisture from the adhesive too quickly, resulting in loss of strength and performance of the final bond. Very dense surfaces can have the opposite effect, taking a long time for the window of receptiveness to open, which can result in flooring being placed too quickly and trapping moisture underneath. These dense surfaces can also struggle with absorbing enough adhesive, meaning they don’t gain enough strength of bond into the surface. Here are some of the most used adhesives for adhering LVT, and their benefits:

Premium adhesives
Most instances would dictate LVT isn’t installed where specialist adhesives are required. However, when installing LVT, owing to the small format modular nature of the tiles, it’s beneficial to have an adhesive which achieves a high-bond strength, presents an early window of receptiveness, and stays receptive for a long time. Premium adhesives provide just that. These types of adhesives may become receptive in as little as five minutes and stay receptive for 60mins or more. This is a considerable amount of usable time for the installers, who can then spread more area and get into the adhesive sooner. These adhesives will also provide good slip-resistance when placing tiles, a valuable attribute for all installers of LVT flooring.

Pressure sensitive adhesives (PS)
Always a popular choice, and generally come with some great attributes. They’re easy to apply and can remain receptive for a very long time. Sometimes, they can be left too long, and placing LVT into PS adhesive too late won’t provide a transfer of adhesive onto the tile backing. When adhering flooring to traditional bases, like smoothing compounds or timber substrates, PS adhesive is used much in the same fashion as most other acrylic adhesives which requires a short waiting time before placing the flooring and allowing a full transfer of adhesive. Allowing a PS adhesive to go fully clear is only needed in quite specific instances. These instances will be when the adhesive is applied to non-absorbent bases such as terrazzo or metal. The application would then usually require the change of the trowel size used to a smaller notch size. Because non-absorbent bases don’t allow the moisture contained in the adhesive to soak in, if you place a resilient floor covering such as LVT over a semi-wet adhesive, the moisture will become permanently trapped, leading to potential failures. In the case of metal substrates, it can also lead to rusting.

High temperature adhesives (HT)
Installations that may be exposed to significant solar gain will benefit from these types of adhesives. Fluctuations in temperature can cause the floor covering to change dimension multiple times and high-temperature adhesives are specifically designed to resist this. HT adhesives are used in environments where the surface temperature of the floor covering is anticipated to fluctuate significantly. These are usually areas where large format windows are present or intense sunlight falls onto the floor for prolonged periods of time. These adhesives will usually have a very short waiting time before placing the floor covering but, by design, they’ll generally lose their receptiveness much earlier than other types of adhesives. The benefit is that these adhesives form a very strong bond, which enable the LVT to resist movement and remain dimensionally stable.

High strength adhesives (MS, PU & Epoxy)
There are applications where a much higher-strength bond is required, or more comprehensive qualities are needed. These adhesives will provide a much higher sheer-resistance and would commonly be used in areas that experience a large volume of traffic, dynamic loads or where the floor is anticipated to encounter water frequently. These are heavy-duty adhesives which overcome several factors that other standard types of adhesives may struggle to cope with. These adhesives can also be used where the substrate is non-absorbent. Standard adhesives rely upon absorption into the substrate and evaporation into the air to lose water and gain strength, which isn’t the case for these adhesives. They can be a suitable option where the permanent bonding of LVT is need on terrazzo, metal, or acoustic membranes.

Some LVTs aren’t needed to be permanently bonded to the floor, and there’s a large volume of flooring that’s now ‘loose-lay’. These tiles are designed with additional components to provide higher-dimensional stability. This allows them to be held in place with only a tackifier, which allows for the easy removal and replacement of the tiles if needed, especially where raised access flooring is utilised. Tackifiers are adhesives which are designed to be left to fully dry before any flooring material is placed. They’re applied using paint rollers, leaving a thinner film, and achieving maximum surface contact with the flooring. The tackifier effectively grips the product in place.

As you can see, the choice of adhesive is very important when it comes to installing LVT and careful consideration is always needed when selecting the appropriate product.
Steve Thornton is technical manager – wall and floor at Bostik

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